This invention relates in general to metal substrate surface coatings, and in particular to methodology and coated products therefrom for rendering a surface of a metal substrate substantially acid impervious by depositing a mixture of a high-temperature resistant polymer particulate such as polyamide particulate and a curable powder adhesive on the surface of the metal substrate and thereafter curing the adhesive to thereby adhere the polyamide particulate as a film on the surface.
In certain applications it is necessary to provide a substantially acid-impervious metal substrate that comes into contact with another substrate whose chemical acidity acts to leach any available iron from the metal substrate. One important application is found in curing fixtures used to fabricate polymer composite resin-impregnated parts. In particular, resin-impregnated fiber of polymer composite material is placed on a steel curing fixture to give parts made therefrom a desired shape. The composite material is vacuum-bagged to the steel fixture and cured in an autoclave at an elevated temperature, all as known in the art. However, certain high-temperature polymer composite materials that cure above about 500xc2x0 F. will corrode the steel fixture while contemporaneously producing a bad part that exhibits undesirable reduced oxidative properties and high porosity.
It has been found that the reason for the above described corrosion and poor product yield is due to acid from the composite material acting to leach iron from the steel fixture. Because of the resulting untoward effect, it is most important to block acid passage into the fixture to thereby prevent iron leaching into the fabricated part. Accordingly, a primary object of the present invention is to provide methodology for providing a coating to a metal surface such as the surface of a steel curing fixture to thereby render that surface substantially acid impervious.
Another object of the present invention is to provide such methodology wherein the coating is deposited on the metal surface as a mixture of high-temperature resistant polymer particulate such as a polyamide particulate and a curable powder adhesive which thereafter is cured to adhere the polymer particulate as an acid impervious coating on the surface.
Yet another object of the present invention is to provide an acid impervious steel curing fixture having a high-temperature resistant polymer particulate coating thereon which is temperature resistant up to about 700xc2x0 F.
These and other objects of the present invention will be apparent throughout the description thereof which now follows.
The present invention is a method of rendering a surface of a metal substrate substantially acid impervious. The method comprises first placing the surface in a field of treatment, then depositing a mixture of a high-temperature acid-impervious polymer particulate such as polyamide particulate and a curable powder adhesive on the surface, and finally subjecting the surface-coated metal substrate to a curing treatment sufficient to cure the powder adhesive and thereby adhere the polymer particulate as a film on the surface. Preferably, the polymer particulate is acid-impervious up to about 700xc2x0 F., while the powder adhesive in all cases of course cures below the acid-imprevious level of the polymer particulate.
A steel substrate coated in accord with the present methodology is particularly useful as a curing fixture upon which resin-impregnated fiber of polymer composite material is placed to thereby give molded parts made therefrom a desired shape. Production of a part is accomplished by vacuum bagging the composite material to the steel fixture and curing the so-produced part in place on the fixture in an autoclave at an elevated temperature. In this manner the acid impervious curing fixture of the present invention allows production of composite parts without the danger of leaching iron from the fixture to thus assure full-utility part fabrication.